Quality, never quantity!! Not all black belts can teach, nor should all of them try to; either one can or can't...recognizing ones limitations or abilities go a long way.

Very true. As you state, the answer could be one or the other or both or neither.

Time, age, rank, title... none of these factors guarantees the ability, character or maturity to teach. Sad but there it is._________________The person who succeeds is not the one who holds back, fearing failure, nor the one who never fails-but the one who moves on in spite of failure.
Charles R. Swindoll

This is where rank is being placed in the foremost of one's mind whereas rank is thought of as something of undeniable importance to the MAist, instead of it being the furthest thing in one's mind.

We instructors are the guardians of rank, as long as it's content and context is aligned properly. If there's a list of any kind, let rank be kept at the bottom of that list for all times, if it has to be considered.

Whenever a Testing Candidate applies for an upcoming Testing Cycle, the Hombu searches on said candidate's Hard Card, which is filed and kept under lock and key at the Hombu, to determine several factors:

My own Hard Card hasn't followed the SOP's in this regards much, if at all, except for my JBB. For example, I earned my Shindokan Karate-do Hachidan when I was 42 years old, not the prescribed age of 60; that's having my time spent on the floor just a mere 35 years. Inasmuch, I earned my Shindokan Kobudo Hachidan when I was only 51 years old...all under Dai-Soke.

This link might give you an idea how my age rarely followed our By-Laws...